Do they keep changing the way viewer votes work, or are they just freaking *really* slow in revealing it?

They explain the viewer votes every single week.... perhaps you've missed it.

In the same way that the judges votes work.. the couple that got the most viewer votes will get 4 points this week since there's only 4 couples left. The second highest vote getter gets 3 points, the third highest gets 2 points, and the couple with the lowest votes gets 1 point.

Add that to the judges vote from this week.... and you have your point totals. Max 8 this week.